Thread cutting mechanism for lock-stitch sewing machines with oscillating looptaker

ABSTRACT

THREAD CUTTING MECHANISM FOR A LOCKSTITCH SEWING MACHINE WITH OSCILLATING LOOPTACKER COMPRISES A CURVED THREAD CATCHER CARRYING A FLAT CUTTING KNIFE AND BEING MOUNTED FOR OSCILLATING MOVEMENT IN THE DIRECTION OF MOVEMENT OF THE LOOPTAKER. THE THREAD CATCHER IS OPERATED BY AN AUXILIARY SHAFT PARALLEL TO AND OPERABLY CONNECTED WITH THE LOOPTAKER ROCKSHAFT VIA A MULTIPLE MOTION-TRANSMITTING CAM MECHANISM DESIGNED TO EFFECT A TWO-STEP THREAD CATCHING AND CUTTING OPERATION DURING A LOOPTAKER OSCILLATING CYCLE BY FIRST OPERATING THE THREAD CATCHER AXIALLY TO A FAVORABLE POSITION FOR SEPARATING THE BOBBON THREAD AND THE WORK LIMB OF THE NEEDLE THREAD LOOP AND SUBSEQUENT CUTTING OF THE SEPARATED THREADS BY THE CUTTING KNIFE.

Sept. 20, 1971 THREAD CUTTING MECHANISM FOR LOCKSTITCH SEWING MACHINES WITH GSCILLATING LOOPTAKER Filed Sept. 24. 1969 K. HEDEGAARD 2 SheetsSheet 1 T 24% J 0 7 5 N 4s 72 so 84 83 INVI'IN'HN? hR/HEN HEDEG'AAED P 1971 K. HEDEGAARD 3,605,664

THREAD CUTTING MECHANISM FOR LOCKSTITCH SEWING MACHINES WITH OSCILLATING LOOPTAKER Filed Sept. 24, 1969 2 Sheets-Sheet 2 United States Patent 01 fee 3,695,654 Patented Sept. 20, 1971 3,605,664 THREAD CUTTING MECHANISM FOR LOCK- STITCH SEWING MACHINES WITH OSCILLAT- ING LOOPTAKER Kristen Hedegaard, Gentofte, Denmark, assignor to G. M. Pfalf AG., Kaiserslautern am Pfalz, Germany Filed Sept. 24, 1969, Ser. No. 860,706 Claims priority, application Germany, May 13, 1969, P 19 24 281.0 Int. Cl. D05b 6'5 02 US. Cl. 112-252 8 Claims ABSTRACT OF THE DISCLOSURE Thread cutting mechanism for a lockstitch sewing machine with oscillating looptaker comprises a curved thread catcher carrying a fiat cutting knife and being mounted for oscillating movement in the direction of movement of the looptaker. The thread catcher is operated by an auxiliary shaft parallel to and operably connected with the looptaker rockshaft via a multiple motion-transmitting cam mechanism designed to effect a two-step thread catching and cutting operation during a looptaker oscillating cycle by first operating the thread catcher axially to a favorable position for separating the bobbin thread and the work limb of the needle thread loop and subsequent cutting of the separated threads by the cutting knife.

The present invention relates to lockstitch sewing machines of the type having an oscillating looptaker, more particularly to thread cutting mechanism comprising a thread catcher having a separating tip for the separation of the bobbin thread and the work limb of the needle thread loop prior to the cutting of the separated threads by a thread cutting knife.

In a known thread cutting device of this general type, especially adapted for use in group stitch sewing machines having an oscillating looptaker, a thread catcher rotatable in a horizontal plane and disposed between the looptaker and stitching plate of the machine is provided at its free end with two thread-catching tips disposed at different distances from the pivot axis and having an oscillating plane in the vicinity of the stitching point which forms an angle of 45 with the oscillating plane of the looptaker. During operation, the inner tip of the thread catcher, as viewed from the pivot point, passes behind the needle limb of the needle thread loop, to penetrate the latter, while the outer tip passes behind the bobbin thread and work limb of said loop, whereby to force the latter threads into the recess formed by said tips. In order to effect cutting of the threads, the thread catcher is deflected beyond the stitching point for cooperation with a pair of cutting tongs.

Aside from the fact that a safe separation of the threads is difficult to achieve in the first place due to the close spacing of the threads, an especially serious drawback of the known thread catching and cutting devices and resultant frequent failures of the thread separation is due to the fact that the two limbs of the needle thread loop can be safely separated within a relatively short time interval only, that is, while the tip of the thread catcher intersects the plane of movement of said limbs. In addition, the limbs of the needle thread loop assume a position favorable for the separation during a relatively short interval only within the movement of the loop. This interval begins at the instant when the needle thread loop has been cast to its full Width about the looptaker and ends near the instant when the limbs of the loop have reached the oscillating axis of the looptaker, that is, before the distance between the needle limb of the loop and bobbin thread has become insuflicient to ensure a safe separation of the threads by the tip of the thread catcher.

As a consequence, an essential difficulty in the control of the thread catcher movement in relation to the movement of the needle thread loop is due to the fact that the instant of complete widening of the loop depends upon numerous other factors, such as factors affecting the tension and friction of the needle thread, and is subject to frequent variations and changes of these factors, such as upon changing the type or quality of the thread or work being operated on. Under these conditions, it is for instance possible that the limbs of the needle thread loop have not yet reached or passed the position favorable for safe thread separation and cutting at the start of the operation of the thread catching and cutting device.

In recognition of the foregoing difficulties and drawbacks, it has already been proposed to dispense with the thread separation by seizing the bobbin thread at a time when the needle thread is still above the stitching plate and by cutting the needle thread at a point above the work or exterior of the operating range of the bobbin thread. Aside from the fact that this requires two separate cutting devices, another serious disadvantage is due to the fact that visible thread ends are left upon the upper side of the work which, if objectionable, must be manually drawn to the underside so as not to interfere with the appearance of the work.

Accordingly, an important object of the present invention is the provision of improved thread cutting mechanism of the referred to type which is substantially devoid of the foregoing and related difficulties and drawbacks and which may be readily structurally embodied in conventional oscillating looptaker type sewing machines.

Another object of the invention is the provision of thread cutting mechanism of the referred to type by which the influence of the type and quality of the thread or work operated on, as well as of other exterior factors, on the operation of the thread separation is substantially eliminated or minimized.

Still another object of the invention is the creation, between the needle limb of the needle thread loop and the bo'bbin thread of an oscillating looptaker sewing machine of the referred to type of an adequate free space at right angle to the looptaker oscillating plane, to enable the bobbin thread and work limb of said loop to be readily separated from the needle limb of said loop by the thread catcher moving in a direction parallel to the plane of movement of the needle thread loop.

The invention, both as to the foregoing and ancillary objects as well as novel aspects threreof, will be better understood from the following detailed description, taken in conjunction with the accompanying drawings forming part of this disclosure and in which:

FIG. 1 is a side elevation of an oscillating looptaker type sewing machine embodying improved thread separating and cutting mechanism according to the invention;

FIG. 2. is a partial perspective view more clearly showing the construction and operation of the thread catcher of FIG. 1;

FIG. 3 is a side view of the oscillating looptaker and the thread catcher of the machine according to FIG. 1, shown in the position of the parts immediately prior to the axial displacement of the thread catcher;

FIG. 4 is a perspective view of the multiple cam controlling the operation of the thread catcher;

FIG. 5 is a side view of the cam according to FIG. 4;

FIG. 6 is a plan view of the thread catcher and the needle and bobbin threads in relation to the stitching hole, the parts being shown in the position at the instant immediately prior to the operation of the thread catching and cutting device;

FIG. 7, being similar to FIG. 6, shows the parts in the axially shifted position of the thread separating and cutting step.

FIG. 8 being similar to FIG. 6, shows the parts in the end position of the thread separating and cutting step.

Like reference numerals denote like parts throughout the different views of the drawings.

With the foregoing objects in view, the invention involves generally the subdivision of the separating operation of the thread catcher into two partial steps or movements, viz, a first step to displace the bobbin thread towards the work limb of the needle thread loop in a direction at right angle to the looptaker oscillating plane, on the one hand, and a second step to effect penetration of the separating tip of the thread catcher into the needle thread loop in a direction parallel to the looptaker oscillating plane, on the other hand.

By the subdivision of the thread catching operation into two sequential steps in different directions, the operation of the thread catcher can be controlled in an optimal manner such as to ensure a safe thread separation in respect to the movement of the needle thread loop, provided that the first operating step at right angle to the looptaker oscillating plane is synchronized with the interval during which the needle thread loop in passing around the bobbin case has a maximum angular distance from the bobbin thread and that the second operating step in the direction parallel to the looptaker oscillating path is commenced after the needle thread loop has been expanded to the full width of the looptaker. Since the second operating step is parallel to the plane of movement of the needle thread loop, the angular distance between the two limbs is sufficient, even prior to the final expansion of the loop, to ensure a safe separation of the threads. As a consequence deviations of the thread movement and other factors resulting in a later expansion of the loop, have substantially no effect on the thread separation.

For reasons evident from the foregoing, optimal correlation between the movement of the thread catcher and needle thread loop or maintenance of a definite and constant relationship between the looptaker and thread catcher operations, is highly desirable or required. For this purpose, the thread catcher, according to a preferred embodiment of the invention, is supported by an axially displaceahle auxiliary control shaft arranged parallel to the looptaker rockshaft and having secured thereto a lever carrying a pair of cam follower rollers adapted to cooperate with a multiple control cam fast on the looptaker shaft. The control cam has a first lateral or axially effective cam section for effecting the first or axial thread catcher operating step and a second radially effective cam section for effecting the second thread catcher operating step, respectively.

This method of operating and controlling the thread catcher by the rockshaft of the sewing machine ensures the thread separation to be effected essentially under constant operating conditions, since the number of revolutions of the sewing machine and in turn the angular speed of the looptaker rockshaft, being controlled by the drive shaft during a thread catching and cutting operation, remain at a constant ratio to one another. In contrast, in known automatic sewing machines the thread separating and cutting devices are controlled by the work feed means of the machine. In such a case, if the transmission ratio between the driving armshaft and the feed control cam is varied, a change results in the time interval available for the thread catching and cutting operations. Besides, in the known machines the size of the cam section determining the operation of the thread catching device is directly proportional to the angular range of the cam section controlling the feed movement during a stitching cycle. From this it follows that in case of an increase of the number of stitches during a given sewing program or seam, the cam section controlling the thread catcher must be accommodated within an angularly reduced space, resulting thereby in greater wear of the parts and impairment of the accuracy of the control, in a manner readily understood.

In order to save space for the operating parts of the thread catcher, the threads are severed, during the return oscillating stroke of the thread catcher, by a cutting knife mounted upon the upper side of the thread catcher and having a cutting edge opposed to the thread separating tip. The knife extends advantageously from the side of the thread catcher acting upon the needle limb of the needle thread loop, upwardly in an oblique direction and opposite to the direction of the separating tip, that is, at an angle to the oscillating plane of said loop, in a manner as will become further apparent as the description proceeds in reference to the drawings.

Referring more particularly to FIG. 1, there is shown by way of example, an oscillating looptaker type automatic group-stitch sewing machine, also known as a short seam automat, having embodied therein thread cutting mechanism constructed in accordance with the principles of the invention. The machine comprises essentially a base 1 supporting a sewing table or cloth plate 2 from which extends in a known manner a standard or upright (not visible in the drawing) which terminates in an overhanging arm 3 carrying a sewing head 4. Journalled in the arm 3 is the arm or drive shaft 5 of the machine which carries, at one end, an idler pulley 6 and a drive pulley 7 and which is operably connected, at its opposite end, with both the lever 8 of the thread take-up and the vertically reciprocable needle bar 9 in which is mounted the needle 10, in a manner well known in the art.

Disposed below the stitching plate 11 upon the table 2, provided with the needle or stitching hole 12, FIG. 3, is the oscillating looptaker collectively denoted by numeral 13 and being comprised of the split ring-shaped looptaker race or casing 14, the looptaker proper 15 having a needle thread loop-seizing beak 16 and mounted for oscillation within the race 14, and the bobbin case 17 having a guide finger 18 extending therefrom and being in turn mounted Within the looptaker 15. The latter is actuated in a known manner via a driver 19 by the looptaker rockshaft 20, FIG. 2, said driver being operably connected with the arm shaft 5 via a sliding crank coupling mechanism 23 comprising a crank 21 secured to the end of the looptaker shaft 20 opposite to the driver 19, a sliding block 22 rotatively mounted upon said crank and a guide fork 24 embracing said block and secured to an oscillating or rockshaft 25. Pork 24 has an extension forming a crank 26 to which is jointed the lower end of a connecting rod 27 the upper end of which is journalled in a double-cranked section of the arm-shaft 5.

As a consequence of the operative connections described in the foregoing, the driver 19 is oscillated by the shaft 20, whereby to have its opposite ends alternately engage a pair of abutments of the looptaker 15, in such a manner as to oscillate the latter in synchronism with the reciprocating needle 10 for the production of lockstitches in the work being operated on, adequate play or lost-motion being provided between said driver and said abutments, to enable a ready escape of the needle thread loop upon being cast about the looptaker 15 and pulled in the upward direction by the thread take-up 8, in a manner well known from the operation of oscillating looptaker type lockstitch sewing machines.

The work operated on is held in position by a work clamp 28 having its end opposite to the stitching point (hole 12) mounted in a known manner for horizontal rotation upon a slide block (not shown) arranged to move within a guide slot in the cloth plate 11 parallel to the arm 5. The feed movements of the clamp 28 are effected by means of a control disk 29 mounted upon the front of the upright and/or the arm 3 and being continuously driven by the armshaft 5. Disk 29 has a first cam groove 30 upon its front face serving to control the rotative displacement of the clamp 28 and a second cam groove (not shown) upon its rear face, to control the longitudinal displacement of the slide block supporting the clamp 28. Besides, disk 29 is provided upon its front face with a concentric recess 31 upon the inner periphery of which is disposed a trip or control cam 33.

The automatic stoppage mechanism of the sewing machine, collectively denoted by numeral 34, comprises a control lever 35 to which is secured a braking lever 36, both said levers being urged in the direction of the drive pulley 7 by a tension spring 37.

Secured to the upper end of the lever 35 is a braking and locking element 39 coupled with a buffer mechanism 38 and arranged to cooperate with a braking cam disk 40 fast upon the armshaft 5. Secured to the lower end of the elever 35 is a toothed locking element 41 engaged by a pawl 42 during the operation of the sewing machine.

As a consequence, the braking lever 36 together with the lever 35 are normally held in a deflected position against the action of the spring 37, as shown in FIG. 1. In this position, that is, during the operation of the sowing machine, the locking element 39 is disengaged from the cam 40. The pawl 42 is secured to one end of a bell crank lever 43 the opposite end of which carries an actuating element 44, a tension spring 45 serving to exert a force upon the lever 43, whereby to cause, upon starting of the sewing machine, the pawl 42, to engage the element 41 and to maintain element 44 in resilient contact with the periphery 32 of the recess 31 of the disk 29.

There is provided according to the present invention, underneath and parallel to the looptaker shaft 20', a further shaft 46 to the end of which extending to a point below of looptaker 13 is secured an arm 47 extending in spaced relation to the outer surface of the looptaker case 14, or to the plane of movement of the needle thread loop while being cast about the bobbin case 17, FIG. 3. Secured to the end of the arm 47 is the thread catcher 48 extending substantially concentrically with the axis of shaft 46 and having its free end shaped to form a threadseparating tip 49 projecting into the space between the loop-taker 13 and the stitching plate 11, FIG. 3. The tip 49 essentially points in the direction of the looptaker beak 16.

The separating tip 49, being displaced laterally from the center line of the thread catcher 48, FIG. 8, in the direction of the edge 50 on the opposite side from the stop mechanism 34, extends, as viewed from said tip, along the edge of the thread catcher 48 on the side of the mechanism 34 at first linearly inwardly, as shown at 51, and thereafter along an arc-shaped indentation 52 forming a transition to an outwardly obliquely extending arcshaped shoulder 53, in turn followed by a shallow recess 54. The edge of the separating tip 49 on the side of the thread catcher opposite to the stop mechanism 34 at first extends obliquely in the outward direction, as shown at 55, to merge, via a slight curve 56, into the edge 50.

In the rest position of the thread catcher 48, the tip 49, as viewed from the driving side of the looptaker 15, is located behind the looptaker or bobbin thread G ascending from the guide finger 18 to the needle hole 12, the latter advantageously coinciding with the center of curvature of the arc-shaped section 52, FIG. 6.

Secured to the upper face of the thread catcher 48, between the tip 49 and the recess 54, is a flat cutting knife 57, FIG. 8, arranged with its cutting edge 58 pointing in a direction away from the tip 49 and extending from the edge 50 obliquely towards the opposite edge of the thread catcher 48 to a point intermediate the shoulder 53 and recess 54.

The knife 57 is directly secured, by means of a screw 59, to the thread catcher 48 at a point adjacent to the tip 49, whereby the knife extends from said point along the tangent to the curved upper face of the thread catcher, to leave a free vertical distance between the cutting edge 58 and the surface of the thread catcher 48, as shown in FIG. 3.

Secured to the looptaker rockshaft 20 is a multiple control cam 60 comprised of a hub 61, FIG. 4, a hub extension 62, a control cam 63 and a holding cam 64 spaced from the cam 63 in the direction towards the looptaker 13. Control cam 63 is concentric 'with the axis of the hub 61 and has a segmental recess 65 extending to the outer surface of said hub. One of the boundary surfaces of the recess 65 extends, in a direction at right angle to and along the axis of the hub 61, from the inner lateral surface of the cam 63 facing the holding cam 64, towards the other surface 67 and the outer lateral surface of the cam, providing thereby a first or lateral cam surface 66. The other boundary surface of the recess 65 extends obliquely to the outer surface of the hub 61 and axially in a direction parallel to the hub axis, providing thereby, in conjunction with a part of the outer surface 68 of cam 63 a second radial cam surface 67.

The segmental holding cam 64, has the same diameter as the control cam 63 and is located on the side of cam 63 adjacent its lateral cam surface 66. One boundary surface 69 of the cam 64, being opposed to and coinciding substantially with the plane of the surface 67 of cam 63, merges into a recess 70 concentric with the hub axis and extending to the outer surface of the hub 61. The other boundary surface 71 of the cam 64 is located approximately opposite to the boundary surface 69 in respect to the hub axis.

Disposed opposite to the cam 60 and secured to the shaft 46 is a lever 72 having two lever arms 73 and 74 extending in the same direction, FIGS. 2 and 5. Lever arm 73 carries, on its side facing the stop mechanism 43 and extending in a direction parallel to the rockshaft 20, a cam follower roller 75 and lever arm 74 carries, on its side parallel to the rockshaft 20, a cam follower roller 76.

In the rest position of the thread cutting device, the roller 75 is positioned, at a slight axial distance between the cams 63 and 64, to resiliently engage the hub 61 by the action of a tension spring 77 acting on the lever 74, while the roller 76 is positioned above the surface of the holding cam 64.

Mounted upon the shaft 46 are a pair of spaced collars 78 and 79, FIG. 2, between which are disposed, in the direction viewed from the lever 72, the end of a coupling member 80 loosely encircling the shaft 46, a pressure washer 81 and a compression spring 82. The opposite end of the member 80 is secured to an axially displaceable rod 83 encircled by a further compressing spring 84 engaging respectively one end of the member 80 and a hearing or support for the rod 83 forming part of the cloth plate 2.

The rod 83 has its end extending into the region of the stoppage mechanism 34 and is connected to the arm 85 of an angular lever 86 whose remaining arm 87 is bent angularly towards the lever arm 85 and resiliently engages, with its inner bent face and during the operation of the sewing machine, FIG. 1, a follower roller 88 mounted upon the toothed locking element 41.

The operation of the sewing machine and thread cutter shown and described herein is as follows.

At the start of the last stitch formation of a seam sewing cycle, trip cam 33, FIG. 1, of the cam disk 29 engages the actuating element 44, whereby to result in an anticlockwise rotation of the lever 43. As a consequence, the pawl 42 is disengaged from the locking element 41, causing thereby the spring 37 to pull the braking lever 36 and with it the shift lever 35 towards the left until the locking element 39 engages the braking disk 40. Simultaneously with the deflection of the shift lever 35, roller 88 is displaced towards the free end of the lever arm 87, FIG. 2, resulting in the rotation of the lever 86. In the end position of the deflection of shift lever 35, the roller 88 assumes a position midway of the lower edge surface 89 of lever arm 87 extending substantially horizontally in this position, whereby slight variations of the angular position of the now essentially vertical shift lever 35 will be without influence upon the position of the lever 86.

Deflection of the lever 86 causes the rod 83 and with it the coupling member 80 to be displaced in the direction of the lever 35. As a consequence, the coupling member 80 transmits its movement to the shaft 46 via the washer 81, compression Spring 82 and collar 79, whereby to displace the shaft 46 in the same direction until the roller 75 engages the inner lateral surface of the cam 63. Further displacement of the member 80 results in a compression of the spring 82, whereby to store energy from the operating movement released by the stoppage mechanism 34 and to be transmitted to the shaft 46 via the coupling member 80, preparatory to the carrying out of a thread cutting operation. The actual separating and cutting movement is effected by the shaft 46 only until the needle has receded from the stitching hole 12 upon seizure of the needle thread and upon the two limbs of the needle thread loop, that is, the needle limb NV and the work limb NN, have reached their maximum angular distance relative to the looptaker or bobbin thread G. This condition exists when the looptaker beak 16 has rotated about 60 from the stitching hole 12 and the limbs NV and NN of the needle thread loop extend tangentially to the circular path of the apex of the loop, as shown in FIG. 3. In correlation therewith, the cam 60 is so adjusted relative to the looptaker shaft 20 as to enable the lateral cam surface 66 to cooperate with the roller 75 at the proper instant, to in turn enable the spring 82 to displace the roller against said surface and along the recess 65. The resultant axial displacement of the shaft 46 in turn causes a displacement of the thread catcher 48 in a direction towards and at right angle to the plane of oscillation of the looptaker 15. As a consequence, the separating tip 49 engages the bobbin thread G ascending to the stitching hole 12, forcing it thereby from its normal position, determined by the stitching hole 12 and the position of the guide finger 18 and coinciding with the plane of movement of the needle limb NV, in a direction towards the work limb NN, in such a manner as to cause the tip 49 at the end of the partial operating step to assume a position about midway between the limbs NV and NN, FIG. 7.

Continued rotation of the looptaker rockshaft causes the holding cam 64, which up to this time has been underneath the roller 76 to avoid a premature deflection of the lever 72, to recede from the operating range of the roller 76, whereby the latter assumes a free position above the recess 70. At the same time, the boundary surface 67 of the recess 65 engages the roller 75, whereby to result in a deflection of lever 76 and with it of the thread catcher 48 whose tip 49 now enters at right angle the thread triangle formed by the two needle thread and work limbs NV and NN. Since the deflection of the thread catcher 48 is parallel to the plane of movement of the limbs NV and NN, the separating step may be extended over a relatively long interval beginning at the instant when the thread catcher has completed its lateral or axial displacement and ending at the instant when the needle thread loop has reached the lowermost point of the bobbin case 17. The deflection of the thread catcher 48 which depends upon the radial distance between the surface of the hub 61 and the surface 68 of the cam 63 is so chosen that the bobbin thread G, in the deflected position of the catcher 48 or with the roller 75 engaging the outer surface 68 of the cam 63, enters the recess 54 to a position in front of the edge 58 of the cutting knife 57.

After the needle thread loop has been cast about the lowermost point of the bobbin case 17, it is pulled in the upward direction by the thread take-up 8, whereby to embrace, as viewed from the tip 49, the underside of the thread catcher 48, FIG. 8, immediately behind the bobbin thread G. As a consequence, the needle limb NV adjoins the edge 50 of the thread catcher 48 and the cutting edge 58 of the knife 57 directly engages the upper face of the thread catcher 48 and extends at a relatively steep angle towards the stitching hole 12, while the work limb NN and the bobbin thread G adjoin the opposite edge of the thread catcher within the recess 54 and pass in front of 8 the obliquely ascending cutting edge in the opposite direction at a relatively shallow angle in the direction towards the stitching hole 12, thereby to intersect the path of the edge 58.

The displacement of the thread catcher 48 thus far described occurs during the forward oscillating stroke of the looptaker 15 in the direction of the beak 16. During the return oscillating stroke of the looptaker, the movement of the thread catcher 48 is reversed, to result in the same operating steps in the opposite direction until reaching of the initial or starting position. As a consequence, the recess 65 is again engaged by the roller and the boundary surface 69 approaches the roller 76. As soon as the concentric part of the cylindrical cam has receded from the roller and the latter is in a position opposite to the recess 65, spring 77 acts to pull the roller 75 in the downward direction and against the hub 61, whereby to deflect the lever 72. At the same time, the boundary surface 69 engages the roller 76, whereby to displace the latter in the upward direction against the outer surface of the holding cam 64. In this manner, the return movement of the lever 72 is effected automatically, whereby to avoid the danger of the spring 77 being unable to return the lever 72 fast enough at the higher velocities of the cam 60 with the result of the roller 75 becoming damaged upon striking the surface 66.

Return of the lever 72 results in the return movement of the thread catcher 48, whereby the cutting edge 58 is forced against the bobbin thread G and the work limb NN, FIG. 2, to sever both the threads prior to the thread take-up lever 8 being able to tension the needle thread.

The thread catcher 48 reaches its starting position at the instant when the thread take-up 9 assumes its upper dead center position within its operating path and the stoppage mechanism 34 acts to arrest the sewing machine. The thread catcher then remains in this position until being returned to its rest position by the bell crank lever 86, rod 83 and coupling member 80 upon re-starting of the sewing machine by operation of the shift lever 35 and braking lever 36.

The mounting of the cutting knife 57 upon the upper side of the thread catcher 48 makes it possible to move the thread catcher at a small distance above the looptaker 13, that is, where the threads have a maximum spacing from each other, while enabling a cutting of the threads at a point closely below the stitching plate 11 and in the vicinity of the stitching hole 12. This results in a minimum of the thread ends protruding from the work after cutting.

The length of the thread protruding from the work can be further reduced by so arranging the knife 57 and cutting edge 58 as to ascend towards the stitching hole 12 at a relatively steep angle and to merge into a restraining tongue guiding the threads towards the cutting edge 58 during the return movement of the return movement of the thread catcher.

The length of the free cut ends of both the bobbin and needle threads required to ensure the safe starting of the first subsequent stitch formation is directly proportional to the width of the thread catcher 48 within the region of the recess 54, on the one hand, and the position of the thread catcher relative to the stitching hole 12, on the other hand. If it is desired to increase the length of the needle thread only, this can be accomplished by a widening of the thread catcher at its longitudinal edge 50. A lengthening of the starting point of the ends of the bobbin and needle threads may be effected by widening of the opposite edge of the thread catcher. In all these cases, the position of the separating tip 49 relative to the stitching hole 12 should remain the same.

The thread cutting device described herein is primarily suited for use in flat-bed sewing machines due to the relatively large distance of the arm 48 from the looptaker 15 in the normal or rest position, such machines providing adequate room between the stitching plate and the looptaker for the mounting of the parts. However, the thread cutting device may be readily adapted by a more compact design for use in sewing machines having an arm-shaped work support Where the parts for severing the threads, that is, the thread catcher 48 and cutting knife 57 may be readily accommodated within the space available within the work supporting arm of the machine, in a manner readily suggesting itself to those skilled in the art.

In the foregoing the invention has been described in reference to an illustrative and exemplary device. It will be evident, however, that variations and modifications as well as the substitution of equivalent parts for those shown and described herein for illustration, may be made without departing from the broader scope and spirit of the invention.

I claim:

1. In combination with a sewing machine having a stitching plate, a reciprocatory needle above said plate, a bobbin and an oscillating looptaker below said plate, and a first rockshaft driven in synchronism with said needle to operate said looptaker for the production of lockstitches in the work operated on, thread cutting mechanism comprising in combination:

(1) a second rockshaft parallel to said first rockshaft,

(2) a curved thread catcher having one end secured to said second rockshaft and having it opposite end terminating in a thread separating tip and arranged to move within the space between said stitching plate and said looptaker in a direction substantially in line with the looptaker oscillating path,

(3) multiple cam and cam follower means operably connecting said first rockshaft with said second rockshaft,

(4) control means to shift said second rockshaft to a predetermined relative axial position, to operate said cam follower means to a starting position relative to said cam and to cause said separating tip to approach the bobbin thread of said looptaker, in a predetermined position of the needle thread loop being cast about said looptaker, preparatory to effecting a forward and return operating stroke of said thread catcher by said second rockshaft via said first rockshaft,

(5) said cam and follower means being designed to at first displace said thread catcher and the bobbin thread axially in the direction towards said looptaker and to subsequently operate said thread catcher through its rotative forward and return operating stroke, to separate the bobbin and needle thread work limb threads from the needle limb of said loop, and

(6) a cutting knife carried by said thread catcher and having a cutting edge pointing in a direction away from said separating tip, to effect cutting of the separated bobbin thread and needle thread work limb during the return stroke of said thread catcher.

2. Thread cutting mechanism as claimed in claim 1, including automatic stoppage means to arrest said machine upon sewing of a predetermined number of stitches, and means to operate said control means by said stoppage means.

3. Thread cutting mechanism as claimed in claim 1, including automatic stoppage means to arrest said machine upon sewing of a predetermined number of stitches, means to operate said control means by said stoppage means, and compression spring means interposed between said stoppage means and said control means, to subsequently axially displace said follower means and said thread catcher.

4. Thread cutting mechanism as claimed in claim 1, said cam means having a first axially effective cam surface and a second radially effective cam surface, to result in the subsequent axial and rotative displacements of said thread catcher.

5. Thread cutting mechanism as claimed in claim 1, said stitching plate having a stitching hole traversed by said needle, and said separating tip being displaced from the median line of said thread catcher in a direction away from and at an oblique angle towards said hole.

6. Thread cutting mechanism as claimed in claim 1, said stitching plate having a stitching hole traversed by said needle, said separating tip being displaced from the median line of said thread catcher in a direction away from and at an oblique angle towards said hole, and said thread catcher having a lateral recess inwardly of said tip, to catch the separated threads in the end position of the forward stroke of the thread catcher.

7. Thread cutting mechanism as claimed in claim 1, said stitching plate having a stitching hole traversed by said needle and said separating tip being displaced from the median line of said thread catcher in a direction away from and at an oblique angle towards said hole, said thread catcher having a lateral recess inwardly of said separating tip, to catch the separated threads in the end position of the forward stroke of the thread catcher, and said cutting knife being arranged between said separating tip and said recess with its cutting edge spaced from the surface of said thread catcher due to the curvature thereof and extending obliquely from a point adjacent the edge near said tip towards and in the direction of said recess.

8. Thread cutting mechanism as claimed in claim 1 wherein said cam includes a cam surface effective to axially displace the second rockshaft, and wherein said axially effective cam surface is in such a position on the first rockshaft that it reaches its first operating position when the beak of the looptaker has rotated about in the forward direction from its uppermost position.

References Cited UNITED STATES PATENTS 3,141,432 7/1964 Reeber et al. 112252 3,173,392 3/1965 Hedegaard 112252 3,371,633 3/1968 Hedegaard ll2-252 FOREIGN PATENTS 832,726 4/1960 Great Britain 112252 JAMES R. BOLER, Primary Examiner 

